Connecting mono to stereo amplifier or stereo to mono amp

[@kougaz]

am i the only one that think that you didn't say how to connect stereo to mono?

[@CoolDudeClem]

I had a pair of computer speakers once that had a mono amp in them, and that amp was connected to both of the speakers. They just shorted both channels together at the connector with no resistors to send a mono signal to the amp, no wonder my sound-card didn't last long! I hate it when someone tries to simulate stereo from a mono recording though, I have a few LP's where there are some mono songs "converted" to stereo and they sound awful through headphones, the original mono recordings sound good enough and should have been left like that.

[@JohnAudioTech]

I have some like that. One channel sounds more treble than the other. I wished they had left it mono. Record companies have been up to stupid tricks for years. Nowadays they feel they must crush the dynamics of music with compression, aka the "loudness wars".

[@rich1051414]

They run the signal through a multi-order crossover, and pan various frequency ranges slightly(hopefully) left and right to simulate different instruments playing in stereo, but it is not realistic at all and only ruins the song. It's especially horrible when a single instrument or voice manages to hit multiple crossed over frequency ranges, and you can hear the sound moving left and right for no reason.

[@MrBrymstond]

Running a stereo signal into two separate mono amps, send the left to one and the right to the other then split the GND to both. Correct?

[@JohnAudioTech]

Yes

[@Tlyrc]

@@JohnAudioTech thanks. I have two very old mono amps like 30+ years old. can i do stereo

[@Tlyrc]

@Moby So the 5.1 is 6 mono amps together?

[@iblesbosuok]

In case mono to stereo, I usually insert a phase shifter circuit. There will be phase difference about 90° between left signal and right signal. Cheers from Indonesia

[@technicaldifficulties3934]

Why to shift the phase and how to avoid impedances and feedback issue between channels

[@BBXFX]

Do you also have a video explaining how to combine the L/R speaker output to a single speaker? For example the 7297 seen in this video powering a single 5-8" subwoofer. Also is it best to filter the frequency before or after the amp? I have seen so many great videos from you, I think it may be covered somewhere...

[@axewax9074]

Brad, This guy doesn't know much, its been a year and he still has not answer your question, a question i was wondering about too plus he should have used a diode with the resistor in his drawing... he does not know much

[@bleem2951]

@@axewax9074 How you would use a diode with a resistor in the input, can you care to elaborate?

[@godofwinetits3826]

can you put diode in each R and L output instead of resistors?

[@BOBBY-w8c]

Good Report. The best I have seen on that issue

[@BOBBY-w8c]

I am Outputting a Phono 1/4" Stereo Headphone Keyboard Signal, into a Guitar Amplifier. Stereo Effect's in the Ketboard Output, are missing. What can I do? I want to connect a Stereo Cable line, to the Amp Input.

[@garthkay-hards2427]

Thanks for this. I was hoping you were going to show us how to input and invert the input on one of the channels for bridge mono mode. Do you have a video for this? Can one use a 1:1 transformer to achieve this?

[@HaimPeretz]

Thanks for the great video! if I have a stereo cable (4 wires: left, right and 2 ground) how can I connect it to this mono amplifier board that has 3 wires: ground , + and - wires? thanks 🙏🏻

[@cezarlixeanu]

does the same happen if I use the bridge connection for a subwoofer amp with a built-in crossover?

[@jayrdeleon625]

Hi thanks for the great video. I got something in mind, can i hook up two mono amp (2 LM1875T Mono) to make it stereo (30wx2)? Thank you again

[@amitghosh6966]

Yes that is possible

[@flhusa1]

could you use diodes of some kind to keep one channel from backfeeding into the other one?

[@JohnAudioTech]

No that would not work and could make heavy distortion.

[@jimmychua7148]

If the source of music is mono and the tone control is stereo and the amplified is mono do i need to put a 1k resistor to the output of tone control thank you.

[@ilyaluv6186]

John, I have a question. What would happen if we raplace (or add to)R1, R2(stereo to mono scheme) with diods?

[@lectrikdog]

Sounds like a Fuzztone, that's what diodes will do: chop out half of your signal

[@vikassm]

@@lectrikdog No diode on the ground, only on the left and right to prevent crosstalk/shorting. Might possibly work!

[@pandaguan]

@@vikassm Diode typically have a forward voltage of 0.7V, so any signal below that would be chopped off.

[@jeffmassey4860]

Add a 1 microfarad poly cap before each resistor (or up to 10ųfd) will help with some d.c. cancellation,and minimize source channel breakdown. But it does add 2 more parts...

[@audioreparaciones8956]

Thank you very much! What about a transformer with two separate primary windings and one secondary winding? Could it be done? Thanks again

[@ghxstxbxrn]

extremely helpful for my project!

[@antonyprasad5536]

Summing amplifier would work perfectly I think.

[@noelj62]

I wonder what happens if you try this mixing matrix: 1) L and R signals pass through a differential op-amp to get the middle channel M. 2) L and R joined to get the stereo image channel S. 3) mix previous channels M+S and try to add a phase shift if necessary.

[@JohnAudioTech]

Differentiating the L and R signals removes common signals (center panned) and is notated as L-R. Joining L and R is summing and is notated as L+R If you now sum L-R and L+R together you get 2L (2 is double the amplitude). If you differentiate L-R and L+R, you end up with 2R. This, BTW, is how FM stereo is decoded as the L+R is sent for compatibility with mono radios and the the L-R signal is also sent. The receiver decodes and does the math to regenerate the L and R channels. It doesn't fix the loud center panned mono issue. Since the center panned information is carried in both L and R channels it would require the remixing of the original multi track session masters to fix that issue.

[@noelj62]

JohnAudioTech You're absolutely right.

[@farisroy_]

Hi, can I use this method for the output?

[@jojofixer]

But my stereo GROUNDS are not common (connected) requiring 4 resistors. Your opinion?

[@fotoamgamgfoto3695]

same here, did you find a solution yet?

[@ConfidenZeTheHumanTorch]

I have a Large Condenser stereo microphone that takes 2 channels on my interface i wanted to go in a dedicated higher quality external mono pre amp with 1 channel then back out as stereo into my interface i thought a y splitter xlr cable would do the trick🤷🏽‍♂️idk i dont want to try until i come up with the best solution the reason i want to d ok this is because the pre amp i wan cost 2k and i cant afford 2 mic pres but i need that specific pre

[@ConfidenZeTheHumanTorch]

( Xlr cables)Stereo Microphone =- mono pre amp channel -= stereo back into [interface]-(thunderbolt into mac)

[@krietor]

@@ConfidenZeTheHumanTorch Once the signal has been converted to mono, you can't convert it back to stereo -well, you can, but the L & R signals will be exactly the same, so there's no point. If you're recording on to the computer using your "interface," then you might as well convert it digitally - duplicate the mono track and assign one copy to L & one copy to R.

[@amitghosh6966]

You mean to say in case of One mono output going into Two stereo channels there's no need to connect resistors from the output to the inputs ?

[@chris1275cc]

Yes, because with mono you effectively only have one signal, when it goes into the amp and gets split into 2 signals both those signals will be identical, so no "imbalance".

[@donvalette3589]

instead of a resistor, cant we use diodes?

[@God-yb2cg]

Also, some lossy codecs at low bitrates that use parametric stereo completely fuck up when you mix them down to mono. You can check by yourself by encoding a stereo music file to opus at 64 or 48 kbps and then mixing down to mono, really not enjoyable musical experience, it can be mitigated by phase shift or very few ms delay between both channels. There would be very few situations where this would be an issue, such as wanting to play some low bitrate stereo files on mono equipment so not a problem for most people.

[@donvalette3589]

Here in argentina we can buy very few modules that are mono. Im trying to make some guitar amps to sell and those stereo module like the same from the video are the only few that we can get. Third world countries find this very usefull xD

[@1oldkaw]

Thank You John, Connecting back and forth between Mono and Stereo. Good topic. Please keep up the good work. I enjoy watching your videos.

[@ali-sleimanchehade6129]

What I would like to know is if the signal is already amplified (output from car head unit) and I want so sum the left and right for a center speaker the head unit is a kenwood and a 22w rms x4 i want to use the left and right front amplified signal to power my single center speaker Please help 🙏

[@JohnAudioTech]

The outputs from the head unit are likely bridged. Output would need to be unbalanced and signal reduced and then mixed into an amplifier for the center speaker.

[@ali-sleimanchehade6129]

@@JohnAudioTech so it’s technically important unless I add a DSP? 😭

[@purplerider2362]

I got NAD 705 from the goodwill for 8 bucks. All I did was use both channels to one speakers signal. I plugged in the negative to the left channel. And the positive to the right channel. I turned it up and it blew out some cheap little Boston speakers. Amp and speakers are fried

[@bid7402]

Great explanation. Exactly what I was looking for.:) What is the value of the resistor you think is suitable for Bluetooth stereo out to be converted to mono? I plan to use one of those USB dongle like Bluetooth Audio Receiver. Thanks in advance.

[@rogerwalter2500]

Biddappa CA 2 resistor of value 1k 0.25 W each for L & R

[@bid7402]

Roger Walter thanks of lot..

[@suseendranbalakrishnan6529]

Hello John Audio Tech, Thanks for this video. I need your suggesstion. I am listening music mostly of the mono recordings, but with stereo cassette deck as well as with CD players connected to the old mono valve radio. In this cable, using with higher impedance 4.7K ohm instead of 1K ohm, will it be good for the mono recording music or will be suppressed ? Are the 4k7 ohms and 4.7K ohms resistors same? Can I use 1% tolerance metal film resistors? Kindly let me know in detail. Thanks again and best regards.

[@abhinb1998]

We Love your work man

[@MrHiram30]

I have a PYLE active sound system model psufm1245A which consists of a single vertical box with two woofers and two tweeters and the amplifier. Although it has two rca inputs for left and right, only one of the inputs produces sound (the red one). If I use a mono to stereo converter, will I be able to hear the stereo sounds through a single output?

[@88s10Durango]

??? So I would like to connect 3 Tpa3116D2 amplifiers to a single stereo input ,, 2 of the amps are mono versions and want to drive my 10 " dual 4 ohm subwoofer , if I connect 1 with ( mono ) the R+ and the L+ to the other mono amp and the ground split between them I`m worried that the voice coils might be fighting each other with different signals ?? Also will there be a loss to the inputs of the amps thanks John ..

[@alastairwaugh6462]

What happens if the resistors are not of sufficient value. I have added 470 Ohm resistors to L and R channel of a stereo BT module, to mix to a mono signal. Would 1k Ohm be significantly better?

[@djbuddy444]

Love u, thanks for saving me a lot of time trying out different ways! Accidentally skipped to exactly what i was looking for explanation. 😂

[@xpto3698]

Congratulations!!! Mono to stereo starts to be danger when you want to split mono to 3,4,5,6...outputs. The current required to feed all these parallel resistences may demage your source.

[@cleaneraz09]

Hey, i hope you are still active youtube member and could help me out:) i have pzi325.2, and want to bridge to drive subwoofer. User manual said to use Y splitter to drive both channels but use ONLY one signal channel. Is it really so? All the internet (different saurces) is telling me to simply connect both input channels and use stereo to drive bridged mono subwoofer.

[@fotoamgamgfoto3695]

hi! how to join the left GND and right GND? THey are separadte things here not the same pin as common gnd, it has R+ R- L+ L- and the negatives are not the same as gnd

[@myideas8743]

I have 5.1 home theatre and sperate input,I have doubt how input L or R two inputs single SW pin,if I input direct,side speakers will not come stereo,if use like you say 1K resistor?I think it will work.

[@danishdart]

Why wouldn't you use diodes instead of resistors if the issue is bleeding into the empty channel when going from stereo to mono?

[@njfulwider5]

I know this is an older video and man is it helpful. But I have a question and hope you can help me. I am learning as I build anything DIY, and recently I started building BT speaker systems. I want to make a small single speaker and I want to make sure I do something like this. In this video, you are using 2 components to create this on the speaker. What if you have an amp with the bt already incorporated on the board like this one in the link-www.amazon.com/TPA3110-Amplifier-Digital-Wireless-Bluetooth/dp/B07PK9FRBD/ref=sr_1_4?keywords=tpa3110&qid=1583968613&sr=8-4 How could I use something like this to get or should i even bother? I'll be using a Dayton Audio ND64-4 for the single speaker build. So I guess I am wondering if you can do anything on the output? Thanks for your time and trouble!!!

[@njfulwider5]

So i just wanted your other video. Do you think if I added the 1-ohm resistor on the output and then paralleled the right and left, I can use it with a single speaker? Then I will get both channels and a good sound out of my single speaker BT build?

[@shahzadaudio7119]

Hi sir, I have 2 amplifier 4 ×4 Tarasistor one is mono 2SC5200 4 tarasistor another have 2 c5200 a1943 how is make it. I have 2 speakers 12 inches Thanks

[@arlovalen]

I hope you don't mind a noob question.... You mentioned in the video about tape or cd player output resistor value should be about 4.7k to feed a mono amp. I wonder what resistor value I should use for a desktop PC speaker/line output?

[@TheRealDanMac]

I have bought an expensive dj set up that only outputs stereo. I have one powered monitor speaker. when I connect the stereo output to the mono speaker with a connector it causes cancellation.. is there a converter I can use to fix this? I tried to follow the video but is a bit to electronics oriented for me to follow 100%

[@azispratama92]

How do i contact u, i have mono bluetooth speaker, and i want to used, the output speaker cable for the input for stereo amplifier, is it possible ?

[@MrTrollBeast]

im trying to split audio signal into 1 stereo amp powering stereo speakers and 1 mono amp powering a subwoofer, how do I do this?

[@azispratama92]

So basically i had to put resistor into output speaker cable first before i connect into stereo amplifier? sorry i left my earphone @ home,

[@techpluslab8744]

Hi John,what about mixing stereo signals to mono using software and then sending it through just left or right channel without shorting unused channel?any issues with that?

[@ravingloony9043]

Excellent Description. Thanks

[@cooperradke3774]

Would it not be better to use a diode instead of a resistor so you have less loss of signal?

[@jonfixalot968]

Is that diagram work on a mini amplifier and mini decoder sir??

[@amitghosh6966]

Can I connect the output of Usb mp3 module to inputs of two different stereo audio amplifiers ?

[@lectrikdog]

Nice explanation. I always wondered why some records are Mono pressings.

[@yvanjarrossay3411]

Hey, i'm kinda new to this, just trying to figure it out by trying things on inexpensive speakers (or some i've got for free). I want to connect a mono speaker to a stereo amp, i checked the impedance and the watts and it looks good, but my question is: following the scheme at 1.24, does it matter which one is negative and which one is positive? and if yes, which one needs to be separated to L/R and which one to G?

[@JohnAudioTech]

Don't connect the L and R outputs together. This can damage the amp. It is better just to use one channel for one speaker and mix to mono at the input.

[@tiitsaul9036]

you forgot to mention another way mixing stereo to mono. to get real funky sound hook one of the stero outputs to mono input ground. then only stero differential is heard. not very practical but sounds interesting.

[@JohnAudioTech]

I use that to get the rear channel effect from stereo for my TV. It works a treat, but sounds odd for straight mono. I made a box that sums, differentiates, left only and right only pass through. I plan to do a video of it at some point.

[@stringzzzz1]

Hello John I can use your help if your out here. I would take any suggestions on how to find out how to breakout an unbalanced stereo cable into two mono ( L & R ) sources. That is.... Normally, that's not a big deal. Except I have two stereo Amps with only one stereo input per Amp each. Which are 3.5 mm. In other words.My goal is to have each Amp get their full mono current source ll possible. One mono cable per amp. No line loss. power driving a left or Right channels and behaving as if, stereo jacks aren't an issue. Mono amps..Separated in a L & R scenario and producing a Stereo .Field. If using Stereo 3.5 output jacks is the thing over mono male jacks.That would be fine. I just don't want to pop something.. Hey... You're doing good work out here... thanks again.

[@JohnAudioTech]

If I follow, just send the L channel and ground to the amp used for left (send the L signal into both its L and R line in the 3.5mm jack. Same for the R signal and R side amp.

[@イエンスヨハンセン]

Ok, so newbie question here - why not stick a couple of diodes in to prevent current sinking? If you are building a 2.1 amp, how do you best combine the .1 bit?

[@user-hd8rs1yn2q]

Because the signal is AC and the diode cuts half of it off.

[@2davydo]

Maybe this explains why when U take the L and R speaker outputs and connect them to a single or pair of speakers and get a surround effect. B/C i always wondered how that effect worked. Maybe U could do a vid on this phenomenon some time?

[@JohnAudioTech]

I use that to get the rear channel from my two channel TV amplifier. Works great.

[@theobarbosa]

Stereo signal in two stereo amps I can split L and R and connect ground in 4 channels?

[@AtulClassics]

🤣🤣🤣🤣🤣🤣🤣🤣

[@alexandrumihaiologu4539]

How can I connect both outputs (Left and Right channel) of Pam8403 to a single speaker?(I want all his power wihout blowing up by merging them).

[@JohnAudioTech]

The 8403 already has bridged outputs so there is no benefit in doing this unless you have a low impedance speaker (such as 2 ohms). It takes current sharing resistors on each output (4 in total) and the inputs are connected together to be sure the signal is identical on both channels.

[@chelong3780]

Stereo mono is good for bridge output power of amplifier

[@bxb590]

I'm suffering. Get on with it.

[@zetaminor77]

thanks for the video. exactly what I was looking for!

[@CharlesMitchellWoodChuckCNC]

Hi John , I am so new to this but your videos are so helpful , Thank you. What I'm trying to do is build a one speaker bluetooth box using the 50w Amp with the Panasonic capacitors you tested in a previous video, is it possible to connect the +R and -L to the speaker and run a jumper line from the +L over to the +R . I'm also only powering the amp with 5v thru the VVC and ground terminals which

[@JohnAudioTech]

Don't connect the outputs together, it may damage the chips. Use a dual voice coil speaker or use one channel for the woofer and the other for a tweeter.

[@lennarttendam9218]

Can I also use this resistor technique at the speaker output? so say I have a small amp which has a left and right channel output, but I want to connect only one speaker, and have both stereo sides on it, will the resistor technique work?

[@JohnAudioTech]

If the speaker is 4 or more ohms, there is little to no benefit to paralleling the channels. If it is a bridged amplifier (like many of the class D boards) it takes four 0.1 ohm resistors. It is better to get a single channel amp or use two speakers.

[@jeroendruwe9061]

Hey John, at 5:08 you are talking about the resistors. How can I find out what I need for a Chromecast audio input?

[@Hrostbjergsorensen]

use 1k or 2k . its not line output

[@joeblow593]

Me thinks diodes would help.

[@SuburbanDon]

It sounds to me like there is no way so sum the stereo signals into one without losing something. Is that the case ?

[@JohnAudioTech]

Summing causes a 6dB "build up" of center panned sounds. This caused problems with stereo recordings on mono equipment back in the day. There were solutions like Heaco CSG encoding that fixed the build up problem but screwed up the stereo image.

[@SurgTT]

So would I be able to use an active low pass filter board that have stereo input to mono output, and split both the mono output ground and signal back into a 2 channel amplifier to power two subwoofers on each channel?

[@JohnAudioTech]

Yes that should be possible.

[@SurgTT]

thanks, it worked, though i'm getting a bit of ground loop noise at half volume on the amp with a small speaker i tested it with, didn't test it with a sub yet

[@CharlesMitchellWoodChuckCNC]

How many watt resistor would you need if I used a 4.7k resistors

[@JohnAudioTech]

Since this is for small signal use, even 1/8w resistors are okay.

[@GurnamSinghchannel]

how to bridge my stereo amplifier if amp is not bridgeable

[@SianaGearz]

Amplifiers are fundamentally non-bridgeable if they employ bridging internally. Bridging is a trick that only works once.

[@jonfixalot968]

Thank you sir

[@vikassm]

Wild question, Instead of a resistor, Do you think a diode would work for mixing stereo into mono? Prevents left & right channels from shorting out since a diode will only allow current in one direction, one could use a beefy diode to reduce coloration etc. Any thoughts?

[@xpto3698]

diodes cuts the waveform, i would like to hear a sample of it

[@vikassm]

@@xpto3698 yeah I figured out this isn't gonna work for music amplifiers :) BUT, I tried it on the preamp to feed a tiny 5w mono guitar amp and it was, well, interesting :)

[@xpto3698]

@@vikassm I Would like to hear, post on youtube if possible = D

[@ProfessorOzone]

I saw a guy connect the +side of the left channel to the -side of the right channel to get mono. Can you explain what's going on there?

[@pgchris87]

I think that is a bridged connection on certain amplifiers output. I am interested to see an explanatory video on that too.

[@chikku168]

thanks for the great information john

[@JREGOR_]

Helpful ♥

[@untrust2033]

Sourse. Nice

[@samirmandal7966]

Hindi

[@timtrial3971]

well explained thank you

[@mpingo91]

Many thanks for that! :)

[@rich1051414]

Also, if you just connect together left and right, if one of the channels is just phase inverted from the other, you won't get anything at all out of the amp, other than jitter and line noise. You should design a comparator circuit to do a proper stereo to mono merger. I have thought about it, but it seems like a lot of work, surely there is a simple way to do it. Perhaps have the left channel serve as the ground for a buffer to buffer in the right channel? That way the right channel having no signal wouldn't sink anything, it just wouldn't add anything to the left. That still wouldn't take care of phase inverted signals though... I suppose you would need logic level gates to selectively buffer only when both channels share the same polarity. Yeah, a lot of work. I wonder how horrible it would sound if you simply stuck a diode on the right channel and only added on the top half of the sine wave.

[@AdarshBenny]

first comment dude

[@Chepecafeteria]

Realy? People don't know that?

[@jeffhess9484]

So, for the mono-to-stereo situation, how do you connect the speaker to the amp?

[@JohnAudioTech]

You really would need to connect a speaker to each channel. For woofer use, you could go dual voice coil. Paralleling the outputs is possible but more involved.